1. Field of the Invention
The present invention relates to a biometric information transmitter for detecting and transmitting a biometric signal of heart beat or the like.
2. Description of the Prior Art
In a background art, there has been developed a biometric information measuring apparatus for measuring biometric information of a person of heart beat, pulse, a number of steps or the like.
For example, as a hear beat meter constituting a kind of a biometric information measuring apparatus, there has been developed a heart beat meter for mounting a biometric information transmitter for detecting a heart beat signal constituting a biometric signal and transmitting a corresponding biometric information signal by wireless to the chest of a user by a chest belt in a state of being brought into press contact therewith, receiving the biometric information by a biometric information receiver in a shape of a wristwatch and displaying the heart beat value.
There is a system of transmitting biometric information in a biometric information transmitter for measuring, processing and transmitting a heart beat signal on a side of the biometric information transmitter, or outputting a corresponding biometric information signal in accordance with the heart beat signal (refer to, for example, JP-A-2002-148369 and JP-A-5-317278).
In both of the systems, it is general to transmit the signal by modulating the signal on a carrier wave normally in order to alleviate an influence of noise from outside, however, according to the former system, an operating processing is carried out on the side of the transmitter and therefore, the latter system is preferable from a view point of simplifying a constitution on the side of the transmitter or the like.
However, also in the latter system, a battery is used exclusively as a power source and therefore, a reduction in power consumption becomes important.
According to the transmitter of the background art, when the carrier wave is outputted in accordance with the heart beat signal, a reduction in power is carried out by utilizing self-excited oscillation. Thereby, a reduction in the power consumption can be carried out.
However, in the self-excited oscillation, a signal level is attenuated in a short period of time and therefore, there poses a problem that when a power source voltage is lowered in accordance with consumption of the battery, a communication distance becomes extremely small.
The invention has been carried out in order to resolve the above-described problem and it is a problem thereof to restrain a communicatable distance from being shortened even when a power source voltage is lowered, in a biometric information transmitter.